U.S. patent number 4,172,257 [Application Number 05/815,830] was granted by the patent office on 1979-10-23 for ground station antenna for satellite communication systems.
This patent grant is currently assigned to Siemens Aktiengesellschaft. Invention is credited to Helmut Mahner.
United States Patent |
4,172,257 |
Mahner |
October 23, 1979 |
Ground station antenna for satellite communication systems
Abstract
A ground station for satellite communication transmission
systems which utilize a beam which is relatively narrow in the
"hour angle direction" and is relatively wide in the "declination
angle direction" so as to prevent interference from satellites on
geostationary orbits and resulting in an antenna which is longer in
the longitudinal direction than it is in the transverse direction,
thus, making it easy to move from place to place without
disassembly.
Inventors: |
Mahner; Helmut (Haar,
DE) |
Assignee: |
Siemens Aktiengesellschaft
(Berlin & Munich, DE)
|
Family
ID: |
5983488 |
Appl.
No.: |
05/815,830 |
Filed: |
July 14, 1977 |
Foreign Application Priority Data
|
|
|
|
|
Jul 20, 1976 [DE] |
|
|
2632615 |
|
Current U.S.
Class: |
342/356 |
Current CPC
Class: |
H01Q
3/00 (20130101); H01Q 21/08 (20130101); H01Q
19/12 (20130101) |
Current International
Class: |
H01Q
19/12 (20060101); H01Q 19/10 (20060101); H01Q
3/00 (20060101); H01Q 21/08 (20060101); H01Q
003/26 () |
Field of
Search: |
;343/840,854,1ST,778,779,DIG.2 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Lieberman; Eli
Attorney, Agent or Firm: Hill, Van Santen, Steadman, Chiara
& Simpson
Claims
I claim as my invention:
1. A ground station antenna for a satellite communications
transmission system via a first satellite, which is aligned with
its axis is the main beam direction at least approximately to the
point determined by the position of the first satellite in
geostationary orbit, characterized in that the radiation diagram of
the antenna (A,A') has a first 3-dB-beam width of between
0.2.degree. and 2.degree. in a first plane (I), and said first
satellite and other satellite are in said first plane and possesses
a second 3-dB-beam width of between 2.degree. and 20.degree. in a
second plane (II) which is at right angles to said first plane (I),
and the ratio of the beam width of the first beam to the second
3-dB-beam being equal to or less than 0.25, and the alignment of
the first plane corresponds approximately with the plane
established by the antenna axis in the main beam direction and a
tangent to the geostationary orbit at the intersection point with
the antenna axis and said ground station antenna comprising four
parabolic reflectors arranged in a straight line, and four
adjustable phase shift devices each having first sides connected to
a common source and having second sides connected to separate ones
of said four parabolic reflectors for precise alignment of the
antenna.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates in general to antenna and in particular to
ground station antenna for a satellite communication system.
2. Description of the Prior Art
As satellite communication transmission systems have become more
and more prevalent, it has become desirable to replace large highly
directive antenna with cheaper and more mobile antennas due to the
extreme cost of the large highly directive antenna.
SUMMARY OF THE INVENTION
The present invention relates to a ground station antenna for a
communication satellite transmission system which can be aligned
with its axis in the main beam direction toward a point
predetermined by the position of the satellite on its geostationary
orbit.
In satellite communication transmission systems, ground stations
provided with relatively small antenna having relatively weak
directivity are being used to an increasing extent. This allows the
cost for a ground station to be considerably reduced over the large
highly directive antenna previously used. Ground stations having
relatively small weakly directive antenna can be transported and
assembled more easily than large highly directive antennas. The
automatic tracking of satellites by the antenna can also be
considerably simplified or even dispensed with entirely in certain
instances. In an extended satellite communication network, simpler
ground stations allow substantial reductions in cost even when the
resulting additional cost for the satellite are considered.
The large number of satellite communication networks in operation
and in the planning stage necessitate that the best possible
exploitation of the frequency ranges be assigned to satellite
broadcasting and of the available satellite locations on the
geostationary orbit. Under these conditions, high gain, sharply
focused antenna must be given preference. Stations provided with
weak focusing antenna will in fact act as interferences to other
satellites or will suffer interference from such satellites. With
equal effective radiated power, weakly focusing antenna will emit
more power and thus more interference power than stations having
more sharply focused antenna. Also, for reception, weakly focused
antennas require a higher power flux density of the electrical
energy emitted from the satellite on the earth's surface. If the
extent of these undesired effects are to remain as limited as
possible any reduction in the antenna dimensions at the ground
stations in systems of this type, is controlled by relatively
narrow limits.
Therefore, the diameters of the reflectors of small antenna
generally are at least three to four meters. Antenna of this type
must be disassembled for transportation. The antenna requires a
supporting structure which supports the reflector to be set up
obliquely in a plane having a predetermined direction (azimuth) and
inclination.
The object of the present invention is to provide a ground station
antenna which is used in a satellite communication network and
provides beam widths of different dimensions in two planes
perpendicular to each other so as to produce good exploitation of
the geostationary orbit of a satellite and provides a lower cost
antenna and the dimensions of the antenna allows it to be
transported in the assembled state or alternatively allow it to be
disassembled and reassembled in a very simple and time saving
manner.
The object of the invention is realized in a ground station antenna
for a satellite communication transmission system which is aligned
with its axis in the main beam direction approximately to the point
determined by the satellite position of its geostationary orbit and
where according to the invention the antenna beam in a first
sectional plane has a radiation diagram wherin the 3-dB-beam width
points are between 0.2.degree. to 2.degree.. In a second sectional
plane at right angles to the first plane, the antenna beam width
has a 3-dB points a beam width of between 2.degree. and 20.degree.
and the ratio of the first to the second 3-dB beam width is equal
to or less than 0.25. The alignment of the first sectional plane
corresponds at least approximately with the plane which is set by
the antenna axis in the main beam direction and by a tangent to the
geostationary orbit in the point of intersection with this
axis.
Antennas having asymmetrical radiation patterns in which the
3-dB-beam widths are different in horizontal and vertical planes
are known in numerous embodiments in the radar technology field.
For example, reference can be made to the book by E. Kramar
entitled "Funksysteme fuer Ortung und Navigation" published by
Berlin Union GmbH, Stuttgart, pages 296 and 297. However, it is not
known in the art to use such antenna having different beam widths
in planes at right angles to each other for relatively small weakly
focused antenna for ground stations in satellite communication
networks.
The object of the present invention is based on the recognition
that in order to achieve optimum exploitation of the geostationary
orbit for a plurality of satellites and so as to avoid mutual
interference between various satellite systems, the beam width need
be only of short dimensions only in that plane which is set by the
antenna axis in the main beam direction and by a tangent to the
geostationary orbit in the intersection point with this axis. This
plane which is at least approximately identical to the first
sectional plane of the radiation diagram of the antenna will be
referred to as "hour angle plane" and the second sectional plane at
right angles thereto will be referred to as the "declination
plane". It is to be realized, of course, that the hour angle and
declination are well known coordinates of the celestial coordinate
system. Therefore, the beam width of the antenna beam only need to
be short in the hour angle plane since the adjacent satellites
which act as interference or can suffer interference lie in this
plane. In the declination plane, on the other hand, it is possible
to widen the antenna beam in order to keep the area and, thus, the
outlay for the antenna sufficiently small so as to be as economical
as possible for the relevant satellite communication system.
Interference from other satellite systems do not occur in the
declination plane.
The surface dimensions of an antenna which exhibits a considerably
different 3-dB-beam width in two-sectional planes at right angles
to each other inherently will exhibit a relatively small ratio of
width to length. An antenna of this type considerably simplifies
transportation which is obviously limited by rail and road profiles
since increased dimensions inonly the longitudinal direction
impedes transportation to a considerably lesser extent than
increased dimensions in two dimensions at right angles to each
other. Thus, with a given transportation profile, the antenna
corresponding to the invention can be easily moved in an assembled
form for antennas having considerable antenna gain values.
In a first preferred embodiment, the antenna is a reflector antenna
whose main reflector represents an oblong, curved dish with a width
to length ratio corresponding to the ratio of the first to the
second 3-dB beam width.
In a second preferred embodiment, the antenna comprises a reflector
antenna having a plurality of group radiators wherein the group
radiators are arranged in a line next to each other.
A particular advantageous variation of the second embodiment,
consists in that the overall arrangement is formed by a plurality
of individual antenna each having approximate rotation symmetrical
radiation diagrams and the individual radiators when arranged next
to one another in a horizontal line allows precise alignment of the
overall antenna by means of adjustable phase shift devices in the
supply lines to the individual radiators. Due to the fact that they
are mounted along a horizontal line, for example on a strip
foundation or on the flat roof of a building, the expensive support
construction which is required for conventional antenna which must
be obliquely position, is superfluous. Also, the various components
of the antenna arrangement of the invention are easily accessible
for repair and maintenance as well as assembly and disassembly.
If the antenna of the invention is to be designed to be steerable
for example because it must be selectively aligned to various
geostationary satellites, it is advantageous to align the axis in
such manner that the main beam direction of the antenna of a ground
station is steered along the geostationary orbit of the satellite,
thus, in the hour angle plane. Due to the considerable beam width
in the declination plane, the antenna generally does not need to be
moved in the declination plane. This also applies to those antenna
which require automatic tracking in that tracking can occur only in
the hour angle direction and need not be adjusted for differences
in declination.
With a reflector antenna having a central radiator, the mobility of
the antenna can be accomplished either by mechanical movement of
the overall antenna or by mechanical movement of its primary
radiator. When the antenna is constructed with group radiators, in
addition to a mechanical movement of the overall antenna, an
electrically controlled beam pivoting of the main antenna lobe is
also possible.
Other objects, features and advantages of the invention will be
readily apparent from the following description of certain
preferred embodiments thereof taken in conjunction with the
accompanying drawings although variations and modifications may be
effected without departing from the spirit and scope of the novel
concepts of the disclosure and in which:
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 schematically illustrates a satellite communication
transmission system;
FIG. 2 illustrates a first exemplary embodiment of a ground station
antenna corresponding to the invention in a satellite communication
transmission system;
FIG. 3 illustrates a further embodiment of a ground station antenna
for a satellite communication system;
FIG. 4 is a sectional view taken on line IV--IV in FIG. 2; and
FIG. 5 is a sectional view taken on line V--V in FIG. 3.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 shows a sphere 1 representative of the earth with a ground
station B mounted thereon. The arc GB represents the geostationary
orbit of a plurality of satellites indicates as S0, S1, S2 and S3,
which are arranged on the geostationary orbit of various satellite
networks. The ground station B cooperates with the satellite S0.
The antenna of this ground station is aligned with its axis in the
main beam direction to the satellite S0. In a first sectional plane
I, which is a plane through which the arc GB approximately passes,
the beam has a 3-dB beam width of between 0.2.degree. and
2.degree.. In a second sectional plane II, which is at right angles
to the first sectional plane I, the antenna has a second 3-dB beam
width of between 2.degree. and 20.degree.. The projection of the
radiation diagram in the first and second sectional planes I and
II, are indicated DI and DII. The first sectional plane I is
referred to as the hour angle plane and coincides as can be seen
from FIG. 1 with the plane which is set by the antenna axis in the
main beam direction and a tangent T to the geostationary orbit GB
at the point of intersection with this axis. In other words in the
direction of the satellites S1 and S2 which are adjacent the
satellite S0, the ground station B antenna has a small width and,
thus, is relatively sharply focused whereas in the direction at
right angles thereto, the focusing is not sharp. The lack of sharp
focusing in the declination plane has virtually no effect upon
interference with the adjoining satellites S1 and S2 as these do
not lie in this plane. The relatively short dimensions of the
antenna in the antenna cross-sectional plane governed by the
declination plane, therefore, does not cause a correspondingly high
degree of interference. Also, due to the fact that the antenna is
not sharply focused in the declination plane, automatic tracking of
the antenna in this plane can be dispensed with as the satellites
will normally pass through the beam of the antenna in the
declination plane without automatic tracking. So as to ensure
sufficiently accurate alignment of the antenna to the satellite S0,
if selective alignment to one of the adjacent satellites S1 to S3
is to be provided it is sufficient to design the antenna B so as to
be moveable only in the hour angle plane.
In a first exemplary embodiment illustrated in FIGS. 2 and 4 of an
antenna A, the antenna comprises a main reflector R which is formed
as an oblong, curved dish as shown in sectional view 4. The main
reflector R has a primary radiator PS located at its center and
produces the desired radiation pattern having different widths as
illustrated in FIG. 1. Thus, in the hour angle plane, the beam is
narrow and in the declination plane at right angles thereto, the
beam is relatively wide. The mobility of an antenna arrangement of
the type illustrated in FIGS. 2 and 4 in the hour angle plane can
be accomplished by simply providing that the dish R is moveable on
the antenna platform along a curved track for example.
FIGS. 3 and 5 illustrate a modified form of an antenna A' which
consists of four rotational symmetrical parabolic main reflectors R
through R4 which have primary radiators Ps1 through Ps4. The
primary radiators are commonly fed by a high frequency source in
such a manner that when the radiation of the reflectors R1 to R4
are combined to form the antenna A' the reflector antenna produce
the desired beam widths of different widths in the hour angle plane
and in the declination plane at right angles thereto. As shown in
FIG. 5, the reflectors R1 to R4 have the same cross-sectional shape
and are rotation symmetrical and are arranged in a straight line.
The erection of the four individual reflector antennas presents no
particular difficulties as they simply must be arranged along a
straight line so as to produce the desired overall radiation
pattern illustrated.
The precise alignment of the antenna A' can be accomplished by
utilizing four adjustable phase shift devices in the individual
feed lines of the individual radiators each of which have one side
connected to a common source and the second sides connected to the
four parabolic reflectors.
Although the invention has been described with respect to preferred
embodiments, it is not to be so limited, as changes and
modifications may be made which are within the full intended scope
as defined by the appended claims.
* * * * *